Asthma is an inflammatory disease of the airways. After allergen exposure, IgE bearing cells, such as mast cells and basophils, are first activated. Later, T lymphocytes enter the airways, are activated by allergen and play a key role in regulating this inflammatory response through the elaboration of cytokines such as IL-4, IL-5 and IFN-gamma. This project seeks to examine the cytokine and mediator profiles of mast cell, basophil and T cell subpopulations that may be involved in the generation of inflammation in asthmatic airways.Using flow cytometry and intracellular staining we examined basophil and T cell cytokine production after allergen activation. Basophils were found to be responsible for 5 times more IL-4 producing cells than were T cells, suggesting that basophils may be a significant source of type 2 cytokines in vivo. Eotaxin is a CC chemokine known to have chemotactic activity, but which has not been reported to have an immunoregulatory function. We examined the effect of eotaxin on Ag driven basophil IL-4 production. Eotaxin alone had no effect, but further increased allergen stimulated IL-4 expression and release 2 to 5 fold. Addition of eotaxin to cultures resulted in a 40 fold left shift in the dose response to Ag. This effect was obtained with physiologic concentrations of eotaxin (10 ng/ml) and was mediated through the CCR3 receptor.Tryptase is a protease mediator produced principally by mast cells. We examined PBMC to determine if other cell populations might also be capable of tryptase expression. Tryptase expression was limited to the basophil population. Surprisingly, basophil tryptase expression varied by more than 100 fold between individuals. In these high expressing individuals, basophil tryptase on a per cell basis was comparable to tissue mast cells. Basophil tryptase expression did not correlate with asthma, asthma severity or the presence of mastocytosis.